Process for preparing synthesis gas

ABSTRACT

Disclosed is a process for producing a synthesis gas by reacting a carbon-containing organic compound with steam and/or carbon dioxide using a catalyst whose carbon deposition activity is considerably suppressed. The catalyst is characterized in that it comprises a carrier formed of a metal oxide, and at least one catalytic metal selected from rhodium, ruthenium, iridium, palladium and platinum and supported on the carrier, in that the catalyst has a specific surface area of 25 m 2 /g or less, in that the electronegativity of the metal ion of the carrier metal oxide is 13.0 or less and in that the amount of the catalytic metal is 0.0005-0.1 mole %, in terms of metal, based on the carrier metal oxide.

TECHNICAL FIELD

The present invention relates to a process for the production of a synthesis gas.

BACKGROUND ART

A synthesis gas is a mixed gas containing hydrogen and carbon monoxide and is widely used as a raw material for the synthesis of ammonia, methanol, acetic acid, etc.

Such a synthesis gas may be produced by reaction of a hydrocarbon with steam and/or carbon dioxide in the presence of a catalyst. In the reaction, however, carbon deposition reactions occur as side reactions to cause carbon deposition which brings about a problem of catalyst poisoning.

The raw materials for the carbon deposition are a carbon-containing organic compound used as a raw material and CO produced in situ. The carbon deposition is accelerated as the partial pressures of these raw materials increase. Therefore, it is possible to reduce the amount of the carbon deposition by increasing the feed amount of steam and carbon dioxide while reducing the reaction pressure. In this case, however, it is necessary to excessively use steam and carbon dioxide in order to reduce the partial pressures of the carbon-containing organic compound and CO, so that several disadvantages are caused. For example, consumption of heat energy required for preheating steam and carbon dioxide increases. Further, costs for the separation of these gases from the product increase. Moreover, since a large reaction apparatus is required, the apparatus costs increase.

JP-A-5-208801 discloses a carbon dioxide-reforming catalyst containing a Group VIII metal supported on high purity, super-fine single crystal magnesium oxide. JP-A-6-279003 discloses a carbon dioxide-reforming catalyst containing a ruthenium compound supported on a carrier composed of a compound of at least one alkaline earth metal oxide and aluminum oxide. JP-A-9-168740 discloses a carbon dioxide-reforming catalyst containing rhodium supported on a carrier formed of a Group II-IV metal oxide or a lanthanoid metal oxide or a composite carrier composed of the above metal oxide and alumina. The reaction experiments using these catalysts are performed under ambient pressure. At a high pressure, which is industrially significant, these catalysts show a high carbon deposition activity and, hence, are not satisfactory as industrially applicable catalysts.

The objects of the present invention are:

(1) to provide a process for the production of a synthesis gas by reaction of a carbon-containing organic compound with steam and/or carbon dioxide, which process can solve a problem of carbon deposition;

(2) to provide a process for the production of a synthesis gas of the above-mentioned type, in which a catalyst having suppressed carbon deposition activity is used.

Other objects of the present invention will be understood from the following description of the specification.

DISCLOSURE OF THE INVENTION

The present inventors have made an intensive study to accomplish the above-described objects and, as a result, have completed the present invention.

In accordance with the present invention there is provided a process for producing a synthesis gas, wherein a carbon-containing organic compound is reacted with steam and/or carbon dioxide in the presence of a catalyst, characterized in that said catalyst comprises a carrier formed of a metal oxide, and at least one catalytic metal selected from rhodium, ruthenium, iridium, palladium and platinum and supported on said carrier, in that said catalyst has a specific surface area of 25 m²/g or less, in that the electronegativity of the metal ion of said carrier metal oxide is 13.0 or less and in that the amount of said catalytic metal is 0.0005-0.1 mole %, in terms of metal, based on said carrier metal oxide.

The catalyst used in the present invention (hereinafter referred to also as catalyst of the present invention) contains at least one catalytic metal selected from rhodium (Rh), ruthenium (Ru), iridium (Ir), palladium (Pd) and platinum (Pt) supported on a carrier metal oxide having specific characteristics. In this case, the catalytic metal can be supported in the form of a metallic state or in the form of a metal compound such as an oxide.

The catalyst of the present invention is characterized in that the catalyst has activity required for converting a carbon-containing organic compound into a synthesis gas while exhibiting a function to significantly suppress side reactions of carbon deposition reactions.

The catalyst used in the present invention can significantly suppress the carbon deposition reactions is characterized in that:

(i) the electronegativity of the metal ion of the carrier metal oxide is 13.0 or less;

(ii) the catalyst has a specific surface area of 25 m²/g or less; and

(iii) the amount of the supported catalytic metal is 0.0005-0.1 mole % based on the carrier metal oxide. Such a catalyst having a considerably suppressed carbon deposition activity has been first found by the present inventors.

The metal oxide used as a carrier may be a single metal oxide or a mixed metal oxide. In the present invention, the electronegativity of the metal ion in the carrier metal oxide is 13 or less, preferably 12 or less, more preferably 10 or less. The lower limit is about 4. Thus, the electronegativity of the metal ion in the carrier metal oxide used in the present invention is 4-13, preferably 4-12. The electronegativity of the metal ion in the metal oxide in excess of 13 is not preferable, because carbon deposition occurs significantly.

The electronegativity of the metal ion in the metal oxide is defined by the following formula:

Xi=(1+2i)Xo

wherein

Xi: electronegativity of the metal ion

Xo: electronegativity of the metal

i: valence electron number.

When the metal oxide is a mixed metal oxide, an average electronegativity of the metal ions is used. The average value is a sum of the products of the electronegativity of each of the metal ions contained in the mixed metal oxide by the molar fraction of the corresponding metal oxide of the mixed metal oxide.

The electronegativity (Xo) of a metal is in accordance with Pauling. The electronegativity in accordance with Pauling is as shown in “W. J. Moore Physical Chemistry, Vol. 1 translated by FUJISHIRO, Ryoichi”, 4th Edition, Tokyo Kagaku Dojin, p. 707 (1974), Table 15.4.

The electronegativity of metal ion in a metal oxide is described in detail in, for example, “Shokubaikoza, vol. 2, p145 (1985) edited by Catalyst Society of Japan”.

The metal oxides may include those containing one or at least two metals such as Mg, Ca, Ba, Zn, Al, Zr and La. Illustrative of such metal oxides are single metal oxides such as magnesia (MgO), calcium oxide (CaO), barium oxide (BaO), zinc oxide (ZnO), alumina (Al₂O₃), zirconia (ZrO₂) and lanthanum oxide (La₂O₃), and mixed metal oxides such as MgO/CaO, MgO/BaO, MgO/ZnO, MgO/Al₂O₃, MgO/ZrO₂, CaO/BaO, CaO/ZnO, CaO/Al₂O₃, CaO/ZrO₂, BaO/ZnO, BaO/Al₂O₃, BaO/ZrO₂, ZnO/Al₂O₃, ZnO/ZrO₂, Al₂O₃/ZrO₂, La₂O₃/MgO, La₂O₃/Al₂O₃ and La₂O₃/CaO.

The catalyst used in the present invention having a specific surface area of 25 m²/g or less may be obtained by calcining a carrier metal oxide before the support of a catalytic metal at 300-1,300° C., preferably 650-1,200° C. After the catalytic metal has been supported, the catalytic metal-supported carrier is further calcined at 600-1,300° C., preferably 650-1,200° C. It is also possible to obtain the catalyst by supporting a catalytic metal on a carrier metal oxide, followed by the calcination of the catalytic metal supporting product at 600-1,300° C., preferably 650-1,200° C. The upper limit of the calcination temperature is not specifically limited but is generally 1,500° C. or less, preferably 1,300° C. or less. In this case, the specific surface area of the catalyst or the carrier metal oxide can be controlled by the calcination temperature and calcination time.

The specific surface area of the catalyst or the carrier metal oxide used in the present invention is preferably 20 m²/g or less, more preferably 15 m²/g or less, most preferably 10 m²/g or less. The lower limit of the specific surface area is about 0.01 m²/g. By specifying the specific surface area of the catalyst or the carrier metal oxide in which the electronegativity of the metal ion is 13 or less in the above range, the carbon deposition activity of the catalyst can be significantly suppressed.

The amount of the catalytic metal supported on the carrier metal oxide is at least 0.0005 mole %, preferably at least 0.001 mole %, more preferably at least 0.002 mole %, in terms of metal, based on the carrier metal oxide. The upper limit is generally 0.1 mole %, preferably 0.09 mole %. In the present invention, the amount of metal supported is desirably in the range of 0.0005-0.1 mole %, preferably 0.001-0.1 mole %.

In the catalyst of the present invention, the specific surface area of the catalyst is substantially the same as that of the carrier metal oxide. Thus, in the present specification, the term “specific surface area of a catalyst” is used as having the same meaning as “specific surface area of a carrier metal oxide thereof”.

The term “specific surface area” referred to in the present specification in connection with a catalyst or a carrier metal oxide is as measured by the “BET method” at a temperature of 15° C. using a measuring device “SA-100” manufactured by Shibata Science Inc.

The catalyst used in the present invention has a small specific surface area and has an extremely small amount of a supported catalytic metal so that the carbon deposition activity thereof is considerably suppressed. Yet, the catalyst has satisfactory activity for converting a raw material carbon-containing organic compound into a synthesis gas.

The catalyst used in the present invention may be prepared by conventional methods. One preferred method of preparing the catalyst of the present invention is an impregnation method. To prepare the catalyst of the present invention by the impregnation method, a catalyst metal salt or an aqueous solution thereof is added to and mixed with an aqueous dispersion containing a carrier metal oxide. The carrier metal oxide is then separated from the aqueous solution, followed by drying and calcination. A method (incipient-wetness method) is also effective in which a carrier metal oxide is added with a solution of a metal salt little by little in an amount corresponding to a pore volume to uniformly wet the surface of the carrier, followed by drying and calcination. In these methods, a water soluble salt is used as the catalyst metal salt. Such a water soluble salt may be a salt of an inorganic acid, such as a nitrate or a hydrochloride, or a salt of an organic acid, such as an acetate or an oxalate. Alternately, a metal acetylacetonate, etc. may be dissolved in an organic solvent such as acetone and the solution may be impregnated into the carrier metal oxide. The drying is performed at a temperature of 100-200° C., preferably 100-150° C. when the metal oxide is impregnated with an aqueous solution of a catalytic metal salt. When the impregnation is performed using an organic solvent, the drying is performed at a temperature higher by 50-100° C. than the boiling point of the solvent. The calcination temperature and time are adequately selected according to the specific surface area of the carrier metal oxide or catalyst obtained (the specific surface area of the catalyst). Generally, a calcination temperature in the range of 500-1,100° C. is used.

In the preparation of the catalyst of the present invention, the metal oxide used as a carrier may be a product obtained by calcining a commercially available metal oxide or a commercially available metal hydroxide. The purity of the metal oxide is at least 98% by weight, preferably at least 99% by weight. It is, however, undesirable that components which enhance carbon deposition activity or components which are decomposed under reducing conditions, such as metals, e.g. iron and nickel, and silicon dioxide (SiO₂). Such impurities in the metal oxide are desired to be not greater than 1% by weight, preferably not greater than 0.1% by weight.

The catalyst of the present invention may be used in various forms such as powdery, granular, spherical, columnar and cylindrical forms. The form may be appropriately selected according to the catalytic bed system used.

The production of a synthesis gas according to the present invention may be performed by reacting a carbon-containing organic compound with steam and/or carbon dioxide (CO₂) in the presence of the above-described catalyst. As the carbon-containing organic compound, a lower hydrocarbon such as methane, ethane, propane, butane or naphtha or a non-hydrocarbon compound such as methanol or dimethyl ether may be used. The use of methane is preferred. In the present invention, a natural gas (methane gas) containing carbon dioxide is advantageously used.

In the case of a method of reacting methane with carbon dioxide (CO₂) (reforming with CO₂), the reaction is as follows:

CH₄+CO₂⇄2H₂+2CO  (1)

In the case of a method of reacting methane with steam (reforming with steam), the reaction is as follows:

CH₄+H₂O⇄3H₂+CO  (2)

In the reforming with CO₂, the reaction temperature is 500-1,200° C., preferably 600-1,000° C. and the reaction pressure is an elevated pressure of 5-40 kg/cm²G, preferably 5-30 kg/cm²G. When the reaction is performed with a packed bed system, the gas space velocity (GHSV) is 1,000-10,000 hr⁻¹, preferably 2,000-8,000 hr⁻¹. The amount of CO₂ relative to the raw material carbon-containing organic compound is 20-0.5 mole, preferably 10-1 mole, per mole of carbon of the raw material compound.

In the reforming with steam, the reaction temperature is 600-1,200° C., preferably 600-1,000° C. and the reaction pressure is an elevated pressure of 1-40 kg/cm²G, preferably 5-30 kg/cm²G. When the reaction is performed with a packed bed system, the gas space velocity (GHSV) is 1,000-10,000 hr⁻¹, preferably 2,000-8,000 hr⁻¹. The amount of steam relative to the raw material carbon-containing organic compound is 0.5-5 moles, preferably 1-2 moles, more preferably 1-1.5 moles, per mole of carbon of the raw material compound.

In the reforming with steam according to the present invention, it is possible to produce a synthesis gas in an industrially favorable manner while suppressing the carbon deposition, even when the amount of steam (H₂O) is maintained 2 moles or less per mole of carbon of the raw material compound. In view of the fact that 2-5 moles of steam per mole of carbon in the raw material compound is required in the conventional method, the present invention, which can permit the reforming reaction to smoothly proceed with an amount of steam of 2 moles or less, has a great industrial merit.

In a case where a synthesis gas is produced in the present invention by reacting a carbon-containing organic compound with a mixture of steam and CO₂, the mixing proportion of steam and CO₂ is not specifically limited but is generally such as to provide a H₂O/CO₂ molar ratio of 0.1-10.

The process of the present invention may be carried out with various catalyst systems such as a packed bed system, a fluidized bed system, a suspension bed system and a moving bed system.

EXAMPLE

The present invention will be further described in detail below by examples.

Catalyst Preparation Example 1

The particle size of aluminum oxide calcined at 650° C. for 1.5 h (hour) in air was adjusted to 0.27-0.75 mm. Thereafter, Ru was supported on the aluminum oxide by an impregnation method (incipient-wetness method). This was further calcined at 1,000° C. in air to obtain a Ru-supporting Al₂O₃ catalyst (Ru content was 3.0×10⁻⁴ g per 1 g of Al₂O₃ and, in terms of molar amount, 0.03 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of ruthenium(III) chloride extremely little by little to the calcined Al₂O₃, with mixing by shaking after each dropwise addition. The Ru concentration in the aqueous solution of ruthenium(III) chloride added dropwise was 0.05% by weight. The impregnated material was dried at 120° C. for 2.5 h in air and calcined at 1,000° C. for 1.5 h in the same atmosphere to obtain the Ru-supporting Al₂O₃ catalyst (surface area: 18.6 m²/g). The electronegativity Xi of Al³⁺ of Al₂O₃ is 11.3.

Catalyst Preparation Example 2

The particle size of zirconium oxide calcined at 600° C. for 2 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the zirconium oxide by an impregnation method. This was further calcined at 970° C. in air to obtain a Rh-supporting ZrO₂ catalyst (Rh content was 8.4×10⁻⁶ g per 1 g of ZrO₂ and, in terms of molar amount, 0.001 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined ZrO₂, with mixing by shaking after each dropwise addition. The Rh concentration in the aqueous solution of rhodium(III) acetate added dropwise was 0.0065% by weight. The impregnated material was dried at 120° C. for 2.5 h in air and calcined at 970° C. for 2 h in the same atmosphere to obtain the Rh-supporting ZrO₂ catalyst (surface area: 8.6 m²/g). The electronegativity Xi of Zr⁴⁺ of ZrO₂ is 12.0.

Catalyst Preparation Example 3

The particle size of magnesium oxide (magnesia) calcined at 600° C. for 2 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 1,100° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.6×10⁻³ g per 1 g of Mg and, in terms of molar amount, 0.1 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The Rh concentration in the aqueous solution of rhodium(III) acetate added dropwise was 1.7% by weight. The impregnated material was dried at 120° C. for 2.5 h in air and calcined at 1,100° C. for 2 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 0.6 m²/g). The electronegativity Xi of Mg²⁺ of MgO is 6.6.

Catalyst Preparation Example 4

Rh was supported on magnesium oxide (in the form of ⅛ inch pellets), calcined at 1,100° C. for 3 h in air, by an impregnation method. This was further calcined at 400° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 1.5×10⁻³ g per 1 g of MaO and, in terms of molar amount, 0.06 mol %). The above impregnated material was obtained by soaking the calcined MgO pellets in an aqueous solution of rhodium(III) acetate having a Rh concentration of 1.0% by weight for about 3 h. The impregnated material was then dried at 120° C. for 2.5 h in air and calcined at 400° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 0.7 m²/g). The electronegativity Xi of Mg²⁺ of MgO is 6.6.

Catalyst Preparation Example 5

Rh was supported on magnesium oxide (in the form of ⅛ inch pellets), calcined at 1,100° C. for 3 h in air, by an impregnation method. This was further calcined at 1,000° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.6×10⁻⁵ g per 1 g of MgO and, in terms of molar amount, 0.001 mol %). The above impregnated material was obtained by soaking the calcined MgO pellets in an acetone solution of rhodium(III) acetylacetonate having a Rh concentration of 0.017% by weight for about 3 h. The impregnated material was then dried at 120° C. for 2.5 h in air and calcined at 1,000° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 0.6 m²/g). The electronegativity Xi of Mg²⁺ of MgO is 6.6.

Catalyst Preparation Example 6

Rh was supported on magnesium oxide (in the form of ⅛ inch pellets), containing 5 mol % of calcium oxide and calcined at 1,100° C. for 3 h in air, by an impregnation method. This was further calcined at 950° C. in air to obtain a Rh-supporting CaO/MgO catalyst (Rh content was 7.5×10⁻⁴ g per 1 g of CaO/MgO and, in terms of molar amount, 0.03 mol). The above impregnated material was obtained by soaking the calcined CaO/MgO pellets in an aqueous solution of rhodium(III) acetate having a Rh concentration of 0.5% by weight for about 3 h. The impregnated material was then dried at 120° C. for 2.5 h in air and calcined at 950° C. for 3 h in the same atmosphere to obtain the Rh-supporting CaO/MgO catalyst (surface area: 0.8 m²/g). The average electronegativity Xi of the metal ions of the carrier is 6.5.

Catalyst Preparation Example 7

Rh was supported on magnesium oxide (in the form of ⅛ inch pellets), containing 10 mol % of lanthanum oxide and calcined at 1,100° C. for 3 h in air, by an impregnation method. This was further calcined at 950° C. in air to obtain a Rh-supporting La₂O₃/MgO catalyst (Rh content was 9.0×10⁻⁵ g per 1 g of La₂O₃/MgO and, in terms of molar amount, 0.006 mol %). The above impregnated material was obtained by soaking the calcined La₂O₃/MgO pellets in an acetone solution of rhodium(III) acetylacetonate having a Rh concentration of 0.1% by weight for about 3 h. The impregnated material was then dried at 120° C. for 2.5 h in air and calcined at 950° C. for 3 h in the same atmosphere to obtain the Rh-supporting La₂O₃/MgO catalyst (surface area: 0.8 m²/g). The average electronegativity Xi of the metal ions of the carrier is 6.7.

Catalyst Preparation Example 8

The particle size of magnesium oxide calcined at 1,000° C. for 1.5 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 950° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.6×10⁻⁴ g per 1 g of MgO and, in terms of molar amount, 0.01 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 0.17% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 950° C. for 1.5 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 5.8 m²/g).

Catalyst Preparation Example 9

The particle size of magnesium oxide calcined at 920° C. for 2 h in air was adjusted to 0.27-0.75 mm. Thereafter, Ru was supported on the magnesium oxide by an impregnation method. This was further calcined at 920° C. in air to obtain a Ru-supporting MgO catalyst (Ru content was 1.5×10⁻³ g per 1 g of MgO and, in terms of molar amount, 0.06 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of hydrated ruthenium(III) chloride extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) chloride aqueous solution had a Ru concentration of 1.0% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 920° C. for 2 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 9.6 m²/g).

Catalyst Preparation Example 10

The particle size of magnesium oxide calcined at 300° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Ir was supported on the magnesium oxide by an impregnation method. This was further calcined at 600° C. in air to obtain a Ir-supporting MgO catalyst (Ir content was 4.8×10⁻³ g per 1 g of MgO and, in terms of molar amount, 0.10 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of iridium(IV) chloride extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The iridium(IV) chloride aqueous solution had a Ir concentration of 3.2% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 600° C. for 3 h in the same atmosphere to obtain the Ir-supporting MgO catalyst (surface area: 24.8 m²/g).

Catalyst Preparation Example 11

The particle size of magnesium oxide calcined at 500° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Pt was supported on the magnesium oxide by an impregnation method. This was further calcined at 750° C. in air to obtain a Pt-supporting MgO catalyst (Pt content was 4.8×10⁻³ g per 1 g MgO and, in terms of molar amount, 0.10 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of chloroplatinic acid ([H₂PtCl₆]) extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The chloroplatinic acid aqueous solution had a Pt concentration of 3.2% by weight. The Pt-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 750° C. for 3 h in the same atmosphere to obtain the Pt-supporting MgO catalyst (surface area: 18.4 m²/g).

Catalyst Preparation Example 12

The particle size of magnesium oxide calcined at 300° C. for 3 h in air was adjusted to 1.2-2.5 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 950° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 1.0×10⁻³ g per 1 g of MgO and, in terms of molar amount, 0.04 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 0.68% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 950° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 6.0 m²/g).

Catalyst Preparation Example 13

The particle size of magnesium oxide calcined at 930° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Ru was supported on the magnesium oxide by an impregnation method. This was further calcined at 970° C. in air to obtain a Ru-supporting MgO catalyst (Ru content was 7.5×10⁻⁴ g per 1 g of MgO and, in terms of molar amount, 0.03 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of ruthenium(III) chloride extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The ruthenium(III) chloride aqueous solution had a Ru concentration of 0.50% by weight. The Ru-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 970° C. for 3 h in the same atmosphere to obtain the Ru-supporting MgO catalyst (surface area: 5.2 m²/g).

Catalyst Preparation Example 14

The particle size of magnesium oxide calcined at 350° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 1,050° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.0×10⁻³ g per 1 g of Mg and, in terms of molar amount, 0.08 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 1.3% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 1,050° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 1.5 m²/g).

Catalyst Preparation Example 15

The particle size of magnesium oxide calcined at 950° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Ru was supported on the magnesium oxide by an impregnation method. This was further calcined at 950° C. in air to obtain a Ru-supporting MgO catalyst (Ru content was 2.5×10⁻⁴ g per 1 g of MgO and, in terms of molar amount, 0.01 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of ruthenium(III) chloride hydrate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The ruthenium(III) chloride hydrate aqueous solution had a Ru concentration of 0.17% by weight. The Ru-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 950° C. for 3 h in the same atmosphere to obtain the Ru-supporting MgO catalyst (surface area: 4.8 m²/g). In this case, Ru was found to be supported as ruthenium oxide.

Catalyst Preparation Example 16

The particle size of magnesium oxide calcined at 300° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 1,050° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.3×10⁻³ g per 1 g of MgO and, in terms of molar amount, 0.09 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 1.5% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 1,050° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 2.0 m²/g). In this case, Rh was found to be supported as rhodium oxide.

Catalyst Preparation Example 17

The particle size of magnesium oxide calcined at 1,000° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 950° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 1.5×10⁻⁴ g per 1 g of MgO and, in terms of molar amount, 0.006 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 0.1% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 950° C. for 3 h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 5.6 m²/g).

Catalyst Preparation Example 18

The particle size of magnesium oxide calcined at 500° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh and Pt were supported on the magnesium oxide by an impregnation method. This was further calcined at 1,050° C. in air to obtain a Rh- and Pt-supporting MgO catalyst (Rh and Pt contents were 1.8×10⁻³ g and 4.8×10⁻⁴ g, respectively, per 1 g of MgO and, in terms of molar amount, 0.07 and 0.01 mol %, respectively). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) and chloroplatinic acid ([H₂PtCl₆]) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The mixed aqueous solution had Rh and Pt concentrations of 1.2% by weight and 0.32% by weight, respectively. The Rh- and Pt-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 1,050° C. for 3 h in the same atmosphere to obtain the Rh- and Pt-supporting MgO catalyst (surface area: 1.4 m²/g).

Comparative Catalyst Preparation Example 1

The particle size of magnesium oxide calcined at 370° C. for 3 h in air was adjusted to 0.27-0.75 mm. Thereafter, Rh was supported on the magnesium oxide by an impregnation method. This was further calcined at 370° C. in air to obtain a Rh-supporting MgO catalyst (Rh content was 2.6×10⁻³ g per 1 g of MgO and, in terms of molar amount, 0.10 mol %). The above impregnated material was obtained by adding dropwise an aqueous solution of rhodium(III) acetate extremely little by little to the calcined MgO, with mixing by shaking after each dropwise addition. The rhodium(III) acetate aqueous solution had a Rh concentration of 1.7% by weight. The Rh-impregnated material was dried at 120° C. for 2.5 h in air and calcined at 370° C. for h in the same atmosphere to obtain the Rh-supporting MgO catalyst (surface area: 98 m²/g).

Reaction Example 1

The catalyst (5 cc) obtained in Catalyst Preparation Example 1 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream to convert oxidized Rh into metallic Rh. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 4,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 55% (equilibrium CH₄ conversion under the experimental condition=55%), and the CH₄ conversion at 100 h after the commencement of the reaction was 54%. The term “CH₄ conversion” herein is defined by the following formula:

CH₄ Conversion (%)=(A−B)/A×100

A: mole number of CH₄ in the raw material

B: mole number of CH₄ in the product.

Reaction Example 2

The catalyst (5 cc) obtained in Catalyst Preparation Example 2 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 870° C. and a pressure of 10 kg/cm²G and with GHSV (methane basis) of 2,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 71% (equilibrium CH₄ conversion under the experimental condition=71%), and the CH₄ conversion at 50 h after the commencement of the reaction was 71%.

Reaction Example 3

The catalyst (5 cc) obtained in Catalyst Preparation Example 3 was packed in a reactor to perform a methane reforming test.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂:H₂O=1:0.5:1.0 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 4,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 61.5% (equilibrium CH₄ conversion under the experimental condition=62.0%), and the CH₄ conversion at 400 h after the commencement of the reaction was 61.0%.

Reaction Example 4

The catalyst (20 cc) obtained in Catalyst Preparation Example 4 was packed in a reactor to perform a methane reforming test.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream to convert oxidized Rh into metallic Rh. A raw material gas having a molar ratio of CH₄:CO₂:H₂O=1:0.5:1.0 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 3,500 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 61.0% (equilibrium CH₄ conversion under the experimental condition=62.0%), and the CH₄ conversion at 280 h after the commencement of the reaction was 61.0%.

Reaction Example 5

The catalyst (20 cc) obtained in Catalyst Preparation Example 5 was packed in a reactor to perform a test of reforming methane with H₂O.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:H₂O=1:2 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 2,000 hr⁻¹. The CH₄ conversion and the H₂/CO molar ratio of the product gas at 5 h after the commencement of the reaction were 72.0% (equilibrium CH₄ conversion under the experimental condition=71%) and 4.6, respectively, and the CH₄ conversion at 280 h after the commencement of the reaction was 71.8%.

Reaction Example 6

The catalyst (20 cc) obtained in Catalyst Preparation Example 6 was packed in a reactor to perform a test of reforming methane with H₂O.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:H₂O=1:1 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 5,500 hr⁻¹. The CH₄ conversion and the H₂/CO molar ratio of the product gas at 5 h after the commencement of the reaction were 52.2% (equilibrium CH₄ conversion under the experimental condition=52.3%) and 3.8, respectively, and the CH₄ conversion at 250 h after the commencement of the reaction was 52.0%.

Reaction Example 7

The catalyst (20 cc) obtained in Catalyst Preparation Example 7 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 920° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 4,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 54.0% (equilibrium CH₄ conversion under the experimental condition=55%), and the CH₄ conversion at 380 h after the commencement of the reaction was 53.5%.

Reaction Example 8

The catalyst (5 cc) obtained in Catalyst Preparation Example 8 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream to convert oxidized Rh into metallic Rh. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 850° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 4,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 55% (equilibrium CH₄ conversion under the experimental condition=55%), and the CH4 conversion at 320 h after the commencement of the reaction was 54%.

Reaction Example 9

The catalyst (5 cc) obtained in Catalyst Preparation Example 9 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 870° C. and a pressure of 10 kg/cm²G and with GHSV (methane basis) of 6,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 71% (equilibrium CH₄ conversion under the experimental condition=71%), and the CH₄ conversion at 520 h after the commencement of the reaction was 71%.

Reaction Example 10

The catalyst (5 cc) obtained in Catalyst Preparation Example 10 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 830° C. and a pressure of 5 kg/cm²G and with GHSV (methane basis) of 2,500 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 73% (equilibrium CH₄ conversion under the experimental condition=73%), and the CH₄ conversion at 100 h after the commencement of the reaction was 71%.

Reaction Example 11

The catalyst (5 cc) obtained in Catalyst Preparation Example 11 was packed in a reactor to a methane reforming test.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂:H₂O=1:0.5:0.5 was then treated at a temperature of 880° C. and a pressure of 10 kg/cm²G and with GHSV (methane basis) of 3,000 hr⁻¹. The CH₄ conversion at 5 h after the commencement of the reaction was 70% (equilibrium CH₄ conversion under the experimental condition=70%), and the CH₄ conversion at 120 h after the commencement of the reaction was 67%.

Reaction Example 12

Example 8 was repeated in the same manner as described except that steam was used in lieu of CO₂. The CH₄ conversions at 5 h and 320 h after the commencement of the reaction were 52% and 51%, respectively.

Reaction Example 13

The catalyst (5 cc) obtained in Catalyst Preparation Example 17 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream to convert oxidized Rh into metallic Rh. A raw material gas having a molar ratio of CH₄:CO₂=1:3 was then treated at a temperature of 850° C. and a pressure of 25 kg/cm²G and with GHSV (methane basis) of 6,000 hr⁻¹. After 5 h from the commencement of the reaction, the CH₄ conversion was 86.1% (equilibrium CH₄ conversion under the experimental condition=86.1%) and the CO/H₂ molar ratio of the product gas was 2.2. The CH₄ conversion at 280 h after the commencement of the reaction was 85.7%.

Reaction Example 14

The catalyst (5 cc) obtained in Catalyst Preparation Example 7 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:5 was then treated at a temperature of 830° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 5,500 hr⁻¹. After 5 h from the commencement of the reaction, the CH₄ conversion was 95.7% (equilibrium CH₄ conversion under the experimental condition=95.8%) and the CO/H₂ molar ratio of the product gas was 3.2. The CH₄ conversion at 400 h after the commencement of the reaction was 95.4%.

Reaction Example 15

The catalyst (5 cc) obtained in Catalyst Preparation Example 9 was packed in a reactor to perform a test of reforming methane with CO₂.

The catalyst was previously subjected to a reduction treatment at 900° C. for 1 h in a H₂ stream. A raw material gas having a molar ratio of CH₄:CO₂=1:1 was then treated at a temperature of 800° C. and a pressure of 20 kg/cm²G and with GHSV (methane basis) of 4,000 hr⁻¹. After 5 h from the commencement of the reaction, the CH₄ conversion was 45.5% (equilibrium CH₄ conversion under the experimental condition=45.5%) and the CO/H₂ molar ratio of the product gas was 1.6. The CH₄ conversion at 150 h after the commencement of the reaction was 45.2%.

Comparative Reaction Example 1

A test of reforming methane with CO₂ was performed in the same manner as described in Reaction Example 1 except that the catalyst (5 cc) prepared in Comparative Catalyst Preparation Example 1 was used. In this case, the CH₄ conversions at 5 h and 15 h after the commencement of the reaction were 40% and 8%, respectively.

Comparative Reaction Example 2

A test of reforming methane with H₂O was performed in the same manner as described in Reaction Example 6 except that the catalyst prepared in Comparative Catalyst Preparation Example 1 was used. In this case, the CH₄ conversions at 5 h and 20 h after the commencement of the reaction were 45% and 10%, respectively.

Comparative Reaction Example 3

Methane reforming with CO₂ was repeated in the same manner as described in Reaction Example 15 except that 5 cc of the catalyst obtained in Comparative Catalyst Preparation Example 1 was used. After 5 h from the commencement of the reaction, the CH₄ conversion was 42.0% (equilibrium CH₄ conversion under the experimental condition=45.5%) and the CO/H₂ molar ratio of the product gas was 1.7. The CH₄ conversion at 15 h after the commencement of the reaction was 5.0%.

The catalyst used in the present invention shows considerably suppressed carbon deposition activity, while retaining activity required for converting a carbon-containing organic compound into a synthesis gas. According to the present invention, therefore, a synthesis gas can be produced continuously with a good yield for a long period of time while preventing carbon deposition.

Further, the use of the catalyst of the present invention can effectively suppress the carbon deposition even at a high pressure, so that a small size apparatus of producing a synthesis gas can be used and the device costs can be reduced. 

What is claimed is:
 1. A process for producing a synthesis gas, comprising reacting a carbon-containing organic compound with steam and carbon dioxide in the presence of a catalyst, wherein the amount of steam is 2 moles or less per mole of carbon of said carbon-containing organic compound and 0.1-10 moles per mole of said carbon dioxide, wherein said reaction is performed at a temperature of 600-1000° C., a pressure of 5-40 Kg/cm²G and a GHSV of 1000-10,000 Hr⁻¹, wherein said catalyst consists essentially of a carrier consisting essentially of magnesium oxide, and at least one catalytic metal selected from rhodium and ruthenium and supported on said carrier, wherein said catalyst has a specific surface area of 5.8 m²/g or less, and wherein the amount of said catalytic metal is 0.001-0.08 mole %, in terms of metal, based on said carrier metal oxide.
 2. A process according to claim 1, wherein the specific surface area of said catalyst is 0.01-1.5 m²/g.
 3. A process according to claim 1, wherein said carrier contains at least 98% by weight of magnesium oxide and wherein the amount of impurities selected from Fe, Ni, SiO₂ and mixtures thereof is not greater than 1.0% by weight.
 4. A process according to claim 1, wherein said carrier is obtained by calcining magnesium oxide at a temperature of 950-1,300° C.
 5. A process according to claim 1, wherein said carbon-containing organic compound is natural gas.
 6. A process according to claim 1, wherein said carrier contains at least 98% by weight of magnesium oxide and wherein the amount of impurities selected from Fe, Ni, SiO₂ and mixtures thereof is not greater than 1.0% by weight. 